Science Fair Project Encyclopedia
A Trombe wall is a sun-facing wall built from material that can act as a thermal mass such as stone, concrete, adobe or water tanks combined with an air space, insulated glazing and vents to form a large solar thermal collector. The wall is named after the inventor Felix Trombe , who popularized the design in 1964. Edward Morse had patented the design in 1881.
During the day sunlight shines through the glazing and hits the surface of the thermal mass, warming it by absorption. The air between the glazing and the thermal mass warms (via heat conduction) and rises, taking heat with it (convection). The warmer air moves through vents at the top of the wall and into the living area while cool air from the living area enters at vents near the bottom of the wall.
At night a one way flap on the bottom vent prevents backflow which could act to cool the living area and heat stored in the thermal mass radiates into the living area. These vents are an addition to the original Trombe wall design, which relied entirely on conduction through the thermal mass to transport heat to the living area. In the original design, the vast majority of the heat collected radiates back through the glazing at night.
A major problem with the Trombe wall is that during overcast days or at night the wall acts as a heat loss, completely defeating the intent of the design. This problem is best addressed by adding insulation between the collector space and the thermal mass, and arranging for the thermal mass to be heated by the air circulating through the collector space via the one-way flaps. This change avoids the massive loss of heat at night or on overcast days. Modern passive solar design emphasizes the seperation of collectors and thermal masses.
Common modifications to the Trombe wall include:
- exhaust vent near the top that is opened to vent to the outside during the summer.
- Windows in the trombe wall. This lowers the efficiency but may be done for natural lighting or aesthetic reasons. If the outer glazing has high ultraviolet transmitance and the window in the trombe wall is normal glass this allows efficient use of the ultraviolet light for heating while protecting people and furnishings from ultraviolet radiation when compared to using windows with high ultraviolet transmitance.
- Electric blowers controlled by thermostats.
- Fixed or movable shades.
- Insulating covering used at night on the glazing surface.
- Tubes, pipes or water tanks as part of a solar hot water system.
- Fish tanks as thermal mass.
- Using a selective surface to increase the absorption of solar radiation by the thermal mass.
- Trombe Walls -- NREL page extolling Trombe walls, with no reference to heat loss issues.
- Trombe wall efficiency -- explanation of the problem with Trombe walls.
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